The present invention relates to subterranean treatments and, more particularly, in one or more embodiments, to introducing a water-drainage-rate-enhancing agent into a subterranean formation to enhance gas production following a relative-permeability-modifier treatment to decrease undesired water production.
Hydrocarbon gases (e.g., natural gas) are found in subterranean formations beneath the Earth's surface. To obtain these gases, well bores are drilled into the gas-bearing formations through which the gas is produced to the surface. While gas wells are usually completed in gas-bearing formations, the gas wells may also produce water, for example, due to the water's presence in the producing formation. The higher mobility of the water may allow it to flow into the well bore by way of natural fractures and/or high permeability streaks present in the formation. In addition, because gas is a compressible fluid, the relative permeability to gas is markedly impacted by increasing water saturation. If the water is allowed to flow unrestricted, the water can quickly become the primary fluid flowing through the pore throats, forming what is called a “water block.” Over the life of such wells, the ratio of water to gas recovered may be undesirable in view of the cost of producing the water, separating it from the gas, and disposing of it, which can represent a significant economic loss.
To decrease the production of water, gas wells may be treated with polymers, commonly referred to as “relative-permeability modifiers.” As used in this disclosure, the term “relative-permeability modifier” refers to a polymer that selectively reduces the effective permeability of a subterranean formation to water. In other words, the relative-permeability modifier should substantially reduce the effective permeability of a treated formation to water without a comparable reduction in the effective permeability of the treated formation to hydrocarbons, for example, gas. Because the relative-permeability modifier reduces the formation's effective permeability to water, the production of water from the treated formation should also be reduced. Moreover, due to the selective reduction in permeability primarily to water, gas production from the treated formation should not be adversely impacted. The use of relative-permeability modifiers to decrease the production of water involves less risk than other techniques which involve porosity fill sealants and has the advantage of not requiring expensive zonal isolation techniques.
Following treatment with the relative-permeability modifiers, a gas (such as nitrogen) may be introduced into the treated formation. It is believed that this gas overflush should enhance subsequent gas production from the formation by increasing the gas saturation near the well bore and, in effect, “charging” the formation near the well bore temporarily which should aid in initiating gas flow and clean up of near well bore water blocks. However, treatment with the gas may be difficult, if not impossible, in certain instances, for example, due to logistical problems.